Method of direct plating of copper on a substrate structure

ABSTRACT

The present invention teaches a method for depositing a copper seed layer onto a substrate surface, generally onto a barrier layer. The barrier layer may include a refractory metal and/or a group 8, 9 or 10 metal. The method includes cathodically pre-treating the substrate in an acid-containing solution. The substrate is then placed into a copper solution (pH≧7.0) that includes complexed copper ions and a current or bias is applied across the substrate surface. The complexed copper ions are reduced to deposit a copper seed layer onto the barrier layer. In one aspect, a complex alkaline bath is then used to electrochemically plate a gapfill layer on the substrate surface, followed by overfill in the same bath. In another aspect, an acidic bath ECP gapfill process and overfill process follow the alkaline seed layer process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 60/621,173 [APPM 9762L], filed Oct. 21, 2004, which is hereinincorporated by reference.

This application is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 11/007,857 [APPM 9200], filed Dec. 9, 2004, whichclaims benefit of U.S. Provisional Patent Application Ser. No.60/579,129, filed Jun. 10, 2004. This application is also acontinuation-in-part of co-pending U.S. patent application Ser. No.11/012,965 [APPM 9201], filed Dec. 15, 2004, which claims benefit ofU.S. Provisional Patent Application Ser. No. 60/579,129, filed Jun. 10,2004, and U.S. Provisional Patent Application Ser. No. 60/621,215, filedOct. 21, 2004. This application is also a continuation-in-part ofco-pending U.S. patent application Ser. No. 10/616,097 [APPM 8241],filed Jul. 8, 2003. Each of the aforementioned related patentapplications is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to a method todeposit a metal layer with electrochemical plating and moreparticularly, to the direct plating of a copper layer onto a barrier oradhesion layer.

2. Description of the Related Art

Metallization for sub-quarter micron sized features is a foundationaltechnology for present and future generations of integrated circuitmanufacturing processes. In devices such as ultra large scaleintegration-type devices, i.e., devices having integrated circuits withmore than a million logic gates, the multilevel interconnects that lieat the heart of these devices are generally formed by filling highaspect ratio interconnect features with a conductive material (e.g.,copper or aluminum). Conventionally, deposition techniques such aschemical vapor deposition (CVD) and physical vapor deposition (PVD) havebeen used to fill these interconnect features. However, as interconnectsizes decrease and aspect ratios of device features increase, void-freefilling of interconnect features via conventional metallizationtechniques becomes increasingly difficult. As a result, platingtechniques, such as electrochemical plating (ECP) and electrolessplating have emerged as viable processes for filling sub-quarter micronsized, high aspect ratio interconnect features in integrated circuitmanufacturing processes.

In an ECP process, sub-quarter micron sized high aspect ratio featuresformed into the surface of a substrate may be efficiently filled with aconductive material, such as copper. Most ECP processes are generallytwo stage processes, wherein a seed layer is first formed over thesurface features of the substrate (this process may be performed in aseparate system), and then the substrate surface features are exposed toan electrolyte solution while an electrical bias is simultaneouslyapplied between the substrate and an anode positioned within theelectrolyte solution. The electrolyte solution is generally rich in ionsto be plated onto the surface of the substrate. Therefore, theapplication of the electrical bias drives a reductive reaction to reducethe metal ions and precipitate the respective metal. Upon precipitating,the metal plates onto the seed layer to form a film.

The process requirements for copper interconnects are becoming morestringent, as the critical dimensions for modern microelectronic devicesshrink to 0.1 μm or less. As a result thereof, conventional platingprocesses will likely be inadequate to support the demands of futureinterconnect technologies. Conventional plating practices includedepositing a copper seed layer via physical vapor deposition (PVD),chemical vapor deposition (CVD) or atomic layer deposition (ALD) onto adiffusion barrier layer (e.g., tantalum or tantalum nitride). However,it is extremely difficult to have adequate seed step coverage with PVDtechniques, as discontinuous islands of copper agglomerates are oftenobtained close to the feature bottom in high aspect ratio features withPVD techniques. For PVD techniques, a thick copper layer (e.g., >200 Å)over the field is generally needed to have continuous sidewall coveragethroughout the depth of the features, which often causes the throat ofthe feature to close before the feature sidewalls are covered. For CVDprocesses, copper purity is generally questionable due to difficultcomplete precursor-ligand removal. ALD techniques, though capable ofgiving generally conformal deposition with good adhesion to the barrierlayer, suffer from very low deposition rates for depositing a continuouscopper film on the sidewalls of adequate thickness to serve as a seedlayer

Direct electroplating on barrier materials, such as tantalum or tantalumnitride, is difficult, since these traditional barrier materialsgenerally have insulating native oxides across the surface. Also duringelectroplating, conductive barrier materials (e.g., cobalt) generallywill oxidize near the reductive potential of free copper ions.Therefore, the integrity of the barrier layer may be compromised duringthe electroplating of a copper layer.

PVD has been a preferred technique to deposit a copper seed layer andelectroless plating techniques for depositing a seed layer onto abarrier layer of tantalum or tantalum nitride are known. However, thesetechniques have suffered from several problems, such as adhesion failurebetween the copper seed layer and the barrier layer, as well as theadded complexity of a complete electroless deposition system and theassociated difficulties of process control. In addition, forinterconnect features as small as 32 to 45 nm, it is beneficial toperform the seed layer deposition and the gapfill depositionuninterrupted to prevent formation of oxide or other contamination ofthe seed layer. Furthermore, a well-adhered seed layer has severalbenefits, such as protecting the barrier layer from the acidic solutionsutilized during the electroplating of the bulk copper layer. Also, thecopper seed supports the subsequently deposited bulk copper andminimizes peeling from the barrier layer.

Therefore, there is a need for a process for depositing a copper seedlayer onto a barrier or adhesion layer. The process should deposit thecopper seed layer with a strong adhesion to the underlying layer andwith good uniformity over the entire substrate surface. Also, theprocess should be applicable for a range of barrier/adhesion layermaterials, including cobalt, tungsten, tungsten nitride, titanium,titanium nitride, Ti—W alloy, tantalum, tantalum nitride, ruthenium,Ru—Ta alloy, rhodium, palladium, osmium, iridium and platinum. Further,the barrier or adhesion layer should be maintained with little or nooxidation during seed layer deposition and also should not be chemicallyreduced during the deposition process. Finally, the process should allowthe deposition of a seed layer and a gapfill layer sequentially in thesame plating bath.

SUMMARY OF THE INVENTION

The present invention teaches a method for depositing a copper seedlayer onto a substrate surface, generally onto a barrier layer or anadhesion layer. The barrier or adhesion layer may include a refractorymetal and/or a group VIII metal. The method includes cathodicallypre-treating the substrate surface in an acid-containing solution thatis free of copper ions. The substrate is then placed into a neutral oralkaline (pH≧7.0) copper solution that includes complexed copper ionsand a current or bias is applied across the substrate surface. Thecomplexed copper ions include a carboxylate ligand, such as oxalate ortartrate, or ethylenediamine (ED), EDTA and/or acetate. The complexedcopper ions are reduced to deposit a copper seed layer onto the barrieror adhesion layer. In one aspect, a complex alkaline bath is then usedto electrochemically plate a gapfill layer on the substrate surface,followed by overfill in the same bath. In this aspect, the ECPdeposition of the seed layer, the gap fill layer and the overfill layermay be performed in the same processing chamber. In another aspect, anacidic bath ECP gapfill process is performed on the substrate surface,followed by ECP overfill, also in an acidic plating bath. The copperplating solutions in all embodiments may also contain one or moreadditive compounds, including suppressors, levelers, brighteners andstabilizers.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIGS. 1A-1C illustrate cross-sectional views of a substrate at differentstages of a copper interconnect fabrication sequence.

FIG. 2 illustrates a copper layer formed on a substrate that may becomprised of multiple copper layers deposited by differentelectrochemical plating processes.

FIG. 3 is a graph depicting the relationship of critical current densityon a substrate surface during plating versus sulfuric acid concentrationin the plating bath.

FIG. 4 is a top plan view of an electrochemical processing systemcapable of implementing the methodology of the present invention.

FIG. 5 illustrates a sectional view of an exemplary plating cell andplating head assembly capable of implementing the methodology of thepresent invention.

FIG. 6 is a flow chart of a substrate process sequence for embodimentsof the invention.

For clarity, identical reference numerals have been used, whereapplicable, to designate identical elements that are common betweenfigures.

DETAILED DESCRIPTION

The present invention teaches a method for depositing a copper layeronto a substrate surface, generally onto a barrier or adhesion layer.The barrier layer may include a refractory metal and/or a group VIIImetal. The term group VIII metals (e.g., old CAS system notation) isgenerally intended to describe group 8, 9 and 10 elements, such asruthenium (Ru), rhodium (Rh), palladium (Pd), cobalt (Co), nickel (Ni),osmium (Os), iridium (Ir), and platinum (Pt). The method includescathodically pre-treating the substrate surface in an acid-containingsolution that is free of copper ions. This pre-treatment reduces thecritical current density (CCD) required for forming a continuous andvoid-free seed layer on the barrier or adhesion layer via an ECPprocess. The substrate is then placed into a neutral or alkaline(pH≧7.0) complex copper solution that includes complexed copper ions anda current or bias is applied across the substrate surface. A “complexbath” or “complex solution”, as used herein, is defined as a platingsolution containing at least one complexing, or chelating, compound anda metal ion source, wherein the metal ion source comprises the metal tobe plated on the substrate, e.g. copper. “Alkaline,” as used herein, isdefined as pH≧7.0. The complexed copper ions are reduced to deposit acontinuous, void-free copper seed layer onto the barrier or adhesionlayer. In one aspect, a complex alkaline bath is then used toelectrochemically plate a gapfill layer onto the seed layer, followed byelectrochemical plating of an overfill layer using an acid plating bath.In this aspect, the ECP deposition of the seed layer and the gap filllayer may be performed in the same processing chamber and preferablywith the same plating solution. In another aspect, an acid bath ECP gapfill process is performed on the substrate surface, followed by ECPoverfill, also in an acid bath.

Ruthenium (Ru) thin films, deposited by CVD, ALD or PVD, can be apotential candidate for a seedless interlayer between intermetaldielectric (IMD) and copper interconnect for ≦45 nm technology.“Interlayer”, as used herein, is defined as a layer deposited between adielectric layer and a subsequently deposited metal layer. Examples ofan interlayer include a copper barrier layer, an adhesion layer, and acombined barrier/adhesion layer. Ruthenium is a group VIII metal thathas a relatively low electrical resistivity (resistivity ˜7 μΩ-cm) andhigh thermal stability (high melting point ˜2300° C.). It is relativelystable even in the presence of oxygen and water at ambient temperature.The thermal and electrical conductivities of ruthenium are twice thoseof Tantalum (Ta). Ruthenium also does not form an alloy with copperbelow 900° C. and shows good adhesion to copper. Therefore, thesemiconductor industry has shown an interest in using Ru as aninterlayer layer or adhesion layer. The low resistivity of ruthenium canbe an advantage when trying to fill ruthenium-coated features withcopper without a seed layer. However, because ruthenium layers are oftenvery thin (10-100 Å) and have over three times the electricalresistivity of copper, ruthenium layers still exhibit high sheetresistances, e.g. >20 ohm/square for 100 Å thick ruthenium films. Theterminal effect associated with trying to plate a material on materialsthat have a high sheet resistance can make obtaining uniform, void-freecopper films on 200 and 300 mm substrates problematic.

FIGS. 1A-1C illustrate cross-sectional views of a substrate at differentstages of a copper interconnect fabrication sequence incorporating agroup VIII metal layer. FIG. 1A illustrates a cross-sectional view of asubstrate 100 having metal contacts 104 and a dielectric layer 102formed thereon. The substrate 100 may comprise a semiconductor materialsuch as, for example, silicon, germanium, or gallium arsenide. Thedielectric layer 102 may comprise an insulating material such as,silicon dioxide, silicon nitride, silicon oxynitride and/or carbon-dopedsilicon oxides, such as SiO_(x)C_(y), for example, BLACK DIAMOND™ low-kdielectric, available from Applied Materials, Inc., located in SantaClara, Calif. The metal contacts 104 may comprise, for example, copper,among others. Apertures 120 may be defined in the dielectric layer 102to provide openings over the metal contacts 104. The apertures 120 maybe defined in the dielectric layer 102 using conventional lithographyand etching techniques. The width of apertures 120 may be as large asabout 900 Å and as small as about 400 Å. The thickness of dielectriclayer 102 could be in the range between about 1000 Å to about 10000 Å.

A barrier layer 106 may be formed in the apertures 120 defined in thedielectric layer 102. The barrier layer 106 may include one or morerefractory metal-containing layers used as a copper-barrier materialsuch as, for example, cobalt, titanium, titanium nitride, titaniumsilicon nitride, tantalum, tantalum nitride, tantalum silicon nitride,tungsten, tungsten nitride and Ti—W alloy, among others. The barrierlayer 106 may be formed using a suitable deposition process, such asALD, chemical vapor deposition (CVD) or physical vapor deposition (PVD).The thickness of the barrier layer is between about 5 521 to about 150 Åand preferably less than 100 Å.

As noted above, the barrier layer 106 may instead comprise a thin filmof group VIII metal, such as ruthenium (Ru), a ruthenium-tantalum alloy,rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum(Pt). Such group VIII metal, which is resistant to corrosion andoxidation, may provide a surface upon which a copper layer issubsequently deposited using an electrochemical plating (ECP) process.The group VIII metal may act as a copper-barrier layer. Alternately, thegroup VIII metal may be deposited on the conventional barrier layer,such as Ta (tantalum) and/or TaN (tantalum nitride), to serve as anadhesion layer or other interlayer between the conventional barrierlayer and subsequently deposited copper layers. The group VIII metal istypically deposited using a chemical vapor deposition (CVD) process,atomic layer deposition (ALD) or a physical vapor deposition (PVD)process. Referring to FIG. 1B, a group VIII metal interlayer 108, suchas ruthenium (Ru), is formed on the substrate, and in this example onthe barrier layer 106. The thickness for the group VIII metal interlayer108 often depends on the device structure to be fabricated. Typically,the thickness of the group VIII metal interlayer 108, such as ruthenium,is less than about 1,000 Å, preferably between about 5 Å to about 200 Å.

It has been found that the process of directly plating a metal layer(e.g., copper layer 110) on a barrier 106 that contains pure tantalum(Ta), or tantalum nitride (TaN), will not give good process results. Oneof the problems of plating a metal layer on a pure Ta, or TaN, barrierlayer is due to tantalum's high affinity for oxygen, which causes athermodynamically stable oxide layer to form on the Ta, or TaN, surface,which thus prevents good adhesion between the directly plated metallayer and the Ta, or TaN, barrier layer 106. The adhesion problem istypically found during the direct plating process since the depositedlayer easily separates, or de-bonds, from the surface of the barrierlayer 106. Conventional processing steps that are adapted to remove thesurface oxides on the Ta and TaN, such as aqueous, thermal or plasmaprocesses, which are intended to reduce the formed oxides, are generallyineffective due to rapid re-oxidation of the freshly exposed surfaces.

A Ru—Ta alloy, when used as a group VIII metal interlayer 108 as shownin FIGS. 1A-1C, has the combined benefits of blocking copper diffusionas effectively as conventional tantalum barrier layers and providing asuitable surface for direct plating of a copper seed layer but does notsuffer from the same adhesion problems as found with conventional Ta andTaN barrier layers. Therefore, in one aspect of the invention, thebarrier layer 106 contains a Ru—Ta alloy that contains between about 70atomic % and about 95 atomic % of ruthenium and the balance tantalum. Inanother aspect, the barrier layer preferably contains a Ru—Ta alloy thatcontains between about 70 atomic % and about 90 atomic % of rutheniumand the balance tantalum. In yet another aspect, the barrier layer morepreferably contains a Ru—Ta alloy that contains between about 80 atomic% and about 90 atomic % of ruthenium and the balance tantalum. In oneaspect, it may be desirable to select a Ru—Ta alloy that does notcontain regions of pure ruthenium and/or pure tantalum on the surface.

In some cases, group VIII metal interlayer 108 may also comprise adiscontinuous copper layer, for example a very thin (<100 Å) layer ofPVD copper. Such a copper layer may not be electrically conductive, butmay provide additional nucleation sites for subsequently depositedcopper layers, essentially lowering the effective CCD of the group VIIImetal interlayer.

Referring to FIG. 1C, the apertures 120 may thereafter be filled withcopper layer 110 via one or more direct electroplating processes tocomplete the copper interconnect. Direct plating of copper may beperformed onto a barrier layer 106 or a group VIII metal interlayer 108.However, because it may be beneficial to reduce the critical currentdensity (CCD) required to plate copper onto the substrate surface, i.e.onto barrier layer 106 or group VIII metal interlayer 108, embodimentsof the invention contemplate the application of a cathodic pre-treatmentprocess prior to the deposition of copper layer 110. Critical currentdensity and cathodic pre-treatment are described below in conjunctionwith FIG. 3. Embodiments of the invention further contemplate differentelectroplating methods for the deposition of copper layer 110.

Referring to FIG. 2, copper layer 110 may be comprised of multiplecopper layers deposited by different electrochemical plating processes.For clarity, layers deposited on the substrate prior to copperdeposition, such as dielectric layer 102, metal contacts 104, barrierlayer 106 and group VIII metal interlayer 108, are illustrated togetherin FIG. 2 as conductive substrate surface 114. Copper layer 110 mayinclude a thin, substantially conformal, continuous, void-free layer,hereinafter referred to as a seed layer 111, a gap fill layer 112 and anoverfill layer 113.

In one embodiment, after cathodic pre-treatment of the substratesurface, a seed layer 110 is electrochemically plated onto conductivesubstrate surface 114 using a complex alkaline bath and plating processdescribed below in conjunction with FIGS. 3, 5 and 6. Gap fill layer 112is then electrochemically plated onto seed layer 110 using either acomplex alkaline bath gapfill process, described below in conjunctionwith FIGS. 3, 5 and 6 or a conventional acid bath gapfill process,described below in conjunction with FIGS. 5 and 6. In one aspect, anoverfill layer 113 is then deposited onto gap fill layer 112 with anacid bath ECP process, described below in conjunction with FIGS. 5 and6. An example of an electrochemical plating (ECP) system and anexemplary plating cell are described below in conjunction with FIGS. 4,5 and 6.

Electrochemical Processes

Cathodic Pre-Treatment of Barrier Layer

Embodiments of the invention contemplate a cathodic pre-treatment of asubstrate surface prior to electrochemical plating of copper onto thesurface.

The plating current for a typical ECP process onto a copper seed layeris typically in the range from about 2 mA/cm² to about 10 mA/cm² forfilling copper into submicron trench and/or via structures, such asapertures 120 (shown in FIGS. 1A-1C). However, it has been found that aplating current density of 2-10 mA/cm² will not provide deposition of acontinuous copper film on a ruthenium layer, creating voids. Acontinuous copper film is formed on Ru when the plating current densityis increased and/or the electrolyte resistivity is reduced beyond thevalues used in conventional copper plating. A minimum or criticalcurrent density, or CCD, has been determined wherein plating currentdensities equal to or above this value will form a thin continuouscopper film on a Ru layer and current densities below this value willnot form a thin continuous film on the Ru layer. The magnitude of theCCD is strongly dependent on the resitivity of the plating solution.

FIG. 3 illustrates an example of the CCD versus sulfuric acid (H₂SO₄)concentration. The CCD, as shown in FIG. 3, is defined as the minimumcurrent density required to form a 1000 Å continuous copper film on aruthenium surface. Below the CCD, no visually shiny continuous copperfilm will be deposited at the center regions of the substrate. Themagnitude of CCD is shown to strongly depend on the acidity level of theplating bath.

It is well known that the kinetics of nucleation and crystal growth forelectro-deposition is intimately related to the local electrochemicalover-potential at the nucleation/growth sites as well as the conditionof the surface whereon crystal growth takes place. Over-potential isdefined as the difference between the actual potential and thezero-current (open-circuit) potential. A high over-potential favors newcrystal nucleation by lowering the critical nucleus size and increasingthe density of nuclei, while a low electrochemical over-potential favorsgrowth on existing crystallites. Since the plating current densitydepends on the electrochemical over-potential for a given bath, thecopper deposit structure/morphology is therefore affected by the platingcurrent density. Further, nucleation is also dependent on the “activity”of the substrate surface, i.e., the concentration of “active sites” onthe substrate. Any kind of surface imperfection, such as a crystaldislocation, crystal boundary or incorporated alien atom may serve asthe active site. At the same overvoltage, or at the same applied currentdensity, the amount of nuclei formed will be much higher if the barrierlayer is free from unwanted deposits, such as ruthenium oxides and someorganic compounds, that block the active sites and, hence, inhibitnucleation.

As predicted by theory and confirmed by scanning electron microscopic(SEM) images, a substrate with a copper film plated on a 100 Å Ru filmin a 10 g/l sulfuric acid containing plating solution with a platingcurrent of 3 mA/cm² had large crystallites and poor film deposition inthe center region of the substrate. Measured at the edge of thesubstrate, the thickness of the copper plated film was 1000 Å. Accordingto the results shown in FIG. 3, the CCD is about 40 mA/cm² when thesulfuric acid concentration is 10 g/l. The current density of 3 mA/cm²is much lower than the 40 mA/cm² CCD shown in FIG. 3 and, as expected, anon-continuous layer was formed. It is believed that under this platingcondition, only a few crystallites are stable enough to serve as thenucleation center for further crystal growth, and thus the energy fromthe plating current is primarily used in growing these crystals, withthe help of fast copper adatom surface diffusion. Therefore, the SEMshows large crystallites and copper island deposition in the centerregion of the substrate. To form a continuous copper film across theentire substrate under this condition, the deposited layer would have tobe very thick and the deposited layer would likely contain voids, whichwould make it unsuitable for Cu interconnect applications. Such poordeposition has been found even when the plating current density is onlyslightly lower than the CCD. For example, a substrate that has a 5000 Åthick continuous copper film can be formed on a 100 Å Ru film (depositedby PVD), using a plating solution containing 60 g/l of H₂SO₄ and aplating current density of about 10 mA/cm² (slightly lower than the CCDof 15 mA/cm²). In agreement with theory, however, there were large voidsat the Cu/Ru interface.

Simply increasing plating current density to allow plating of avoid-free, continuous film onto a ruthenium interlayer also hasdisadvantages; generally, a high plating current density tends to resultin poor gap fill. Plating current densities of less than about 10 mA/cm²have been found to encourage bottom-up deposition of trenches and vias,such as apertures 120, with a gap fill layer 112, shown in FIGS. 1A-1C.In order to reduce the plating current density to the range suitable forbottom-up gap fill, the ion concentration of the plating bath may beincreased. For example, it has been shown that a continuous 1000 Åcopper film may be deposited on a 100 Å Ru film on a substrate using aplating bath with a H₂SO₄ concentration of 160 g/l and a plating currentof 5 mA/cm². Referring to FIG. 3, 5 mA/cm² is equal to the CCD for thisparticular acidic concentration. However, cross-section SEM picturesshow that voids were formed at the Cu/Ru interface. When the platingcurrent was raised to 10 mA/cm² (2 times CCD of 5 mA/cm²) and the sameplating bath was used, a continuous 5000 Å copper film was formed on a100 Å Ru layer with no voids at the copper/Ru interface.

One of the reasons for the CCD dependence on bath acidity is related tothe local electrochemical over-potential discussed above. In addition,higher acidity plating solutions may remove unwanted deposits from thesurface and increase the activity of the plating surface. Increasingacid concentration to lower the CCD introduces other problems, however.Because the intention of direct plating is to form a uniform, conformalmetal layer on a barrier layer, electrical conductivity of the bathshould be reduced as much as is practicable. A more conductive platingbath, such as a bath containing a high concentration of acid, degradesthe uniformity of the resultant film.

Recent research presented by Chyan, et al. from University of NorthTexas in American Chemical Society National Meeting in New Orleans, La.,held in Mar. 23 to Mar. 27, 2003, shows that ruthenium oxide (RuO₂) hasa metal-like conductivity, and copper also plates and adheres stronglyto ruthenium oxide. The high CCD's observed on a ruthenium surface couldbe the result of unwanted deposits on the ruthenium surface. “Unwanteddeposits”, as used herein, is defined to include unwanted oxidation of adeposited surface as well as organic contaminants that accumulate on thefresh metallic surface after deposition. A “pure” ruthenium surface isbelieved to be more active for Cu nucleation. Hence, removing theunwanted deposits by a pre-treatment process before copper plating maygreatly reduce the plating current and the plating bath acidity requiredto form a continuous copper layer and avoid voids at the Cu/Ruinterface. Embodiments of the invention contemplate a pre-treatmentprocess that includes a cathodic pre-treatment of the barrier orbarrier/adhesion layer, such as barrier layer 106 or group VIII metalinterlayer 108, as shown in FIGS. 1A-1C.

The cathodic treatment mentioned above is an electrochemical treatmentof a substrate surface in a copper-ion-free acid solution. An oxidizedmetallic surface, particularly a RuO_(x) surface that has formed on afreshly deposited ruthenium barrier/adhesion layer on a substrate, maybe cathodically reduced. Additionally, weakly-bound organic surfacecontaminants may be expelled from the surface by the cathodicpolarization. The removal of these unwanted deposits on the substratesurface prior to electrochemical plating has been demonstrated to reducethe CCD of the barrier/adhesion layer. One possible reduction reactionis shown in equation (1):RuO₂+4H*+4 e⁻→Ru+2H₂O   (1)

The cathodic treatment may be performed in an electrochemical platingcell similar to the copper plating cell described below in associationwith FIG. 5, or in a treatment cell separated from the copper platingsystem. The cathodic treatment cell requires an anode, a cathode and acopper-ion-free acid bath. The acidic concentration range should be inthe range between about 10 g/l to about 100 g/l, and preferably in therange between about 10 g/l to about 50 g/l. A preferred acid is H₂SO₄,but other types of acidic solutions, such as organic sulfonic acidsolutions (e.g. methylsulfonic acid), may also be used. The acidic bathneeds to be free of copper ions to prevent copper deposition on thesurface during the cathodic treatment. Such deposition would be in theform of poorly nucleated copper islands, leading to poor adhesion and/orvoids.

The cathodic treatment can be realized through potential control orcurrent control. With the potential control approach, a referenceelectrode is needed to monitor the wafer potential, in addition to theworking electrodes, which are the thin as-deposited Ru film on the wafersurface, and an anode. Potential control can be realized through apotentiostat. The controlled ruthenium electrode potential, with respectto the reference electrode, is in the range of about 0 volt to about−0.5 volt. In addition to RuO_(x) reduction to ruthenium, H₂ evolutionmay occur on the Ru film surface, hence, it is important to avoidapplying a reduction potential to the substrate that is too high. Withthe current control approach, a cathodic current will be passed betweenthe substrate, coated with a ruthenium film for example, and an anode.The current density should be in the range of about 0.05 mA/cm² to about1 mA/cm². The treatment time should be in the range of about 2 secondsto about 30 minutes. However, in the interest of maintaining adequatethroughput during large-scale processing of substrates, the treatment ispreferably kept below 5 minutes.

Another benefit of cathodically pre-treating a barrier orbarrier/adhesion layer on a substrate, particularly when the layer is agroup VIII metal interlayer 108, is the improved adhesion between copperand the adhesion layer. Experimental results have shown that theadhesion is better between copper and a pre-treated, clean, and possiblyoxide-free ruthenium surface due to a high-integrity Cu/Ru interfacefree of voids. Good interface integrity between the Cu and the Ru layerscan be an important aspect in forming a reliable semiconductor device.Hence, having a pre-treated ruthenium surface is critical to achievehigh quality copper deposition on ruthenium films. Additionally,cathodically pre-treating a ruthenium surface prior to copper platingmay improve the substrate surface's hydrophilicity. The step coverage ofcopper plating on substrate features, such as apertures 120, may beimproved, since the treated surface is more hydrophilic and, hence, moreable to draw the plating solution deep into the features.

The experimental results and discussion related to Ru are merely used asexamples. The inventive concept may also be applied to other group VIIImetals, such as rhodium (Rh), osmium (Os) and iridium (Ir) and barriermaterials, such as cobalt, titanium, titanium nitride, titanium siliconnitride, tantalum, tantalum nitride, tantalum silicon nitride, tungsten,tungsten nitride, a Ti—W alloy, and a ruthenium-tantalum alloy.

Direct Plating on a Barrier Layer with a Complex Alkaline Electrolyte

Embodiments of the invention teach the use of complexed copper sourcescontained within an alkaline plating solution for the direct plating ofcopper layers on barrier and/or barrier/adhesion layers. “Directplating”, as used herein, is defined as the method of electrochemicallyplating a more conductive metal layer, such as seed layer 111 in FIG. 2,onto a substantially less conductive layer, such as conductive substratesurface 114, to facilitate the subsequent uniform, void-free depositionof a gapfill layer 112 and/or an overfill layer 113. This process may beperformed in a plating cell similar to the electrochemical processingcell described below in conjunction with FIG. 5.

A plating solution containing complexed copper sources has asignificantly more negative deposition potential than does a platingsolution containing free copper ions. Generally, complexed copper ionshave a deposition potential from about −1.1 V to about −0.5 V, dependingon the particular complexing agent. Free copper ions have depositionpotentials in the range from about −0.3 V to about −0.1 V, whenreferenced to Ag/AgCl (1 M KCl), which has a potential of 0.235 V versesa standard hydrogen electrode. For example:Cu₂(C₆H₄O₇)+2H₂O→2Cu⁰+C₆H₈O₇+O₂ Δε=−0.7 VCu⁺²+2e ⁻→Cu⁰ Δε=−0.2 V.Further, the current dependence on potential for the complex bath issubstantially reduced when compared to a bath with free copper ions.Therefore, the local current density variation across the substratesurface will be improved, even in the presence of a large potentialgradient across the substrate surface due to the low electricalconductivity of thin barrier metals. This leads to better depositionuniformity across the substrate surface. A more detailed description ofelectrochemical polarization of copper complex baths may be found incommonly U.S. patent application Ser. No. 10/616,097 [APPM 8241], filedJul. 8, 2003, which is hereby incorporated by reference in its entiretyto the extent not inconsistent with the claimed invention.

Suitable plating solutions that may be used with the processes describedherein to plate copper may include at least one copper source compound,at least one chelating or complexing compound, optional wetting agentsor suppressors, optional pH adjusting agents and a solvent.

Plating solutions contain at least one copper source compound complexedor chelated with at least one of a variety of ligands. Complexed copperincludes a copper atom in the nucleus and surrounded by ligands,functional groups, molecules or ions with a strong affinity to thecopper, as opposed to free copper ions with very low affinity, if any,to a ligand (e.g., water). Complexed copper sources are either chelatedbefore being added to the plating solution or are formed in situ bycombining a free copper ion source with a complexing agent. The copperatom may be in any oxidation state, such as 0, 1 or 2, before, during orafter complexing with a ligand. Therefore, throughout the disclosure,the use of the word copper or elemental symbol Cu includes the use ofcopper metal (Cu⁰), cupric (Cu⁺¹) or cuprous (Cu⁺²), unless otherwisedistinguished or noted.

Examples of suitable copper source compounds include copper citrate,copper ED, copper EDTA, among others. A particular copper sourcecompound may have ligated varieties. For example, copper citrate mayinclude at least one cupric atom, cuprous atom or combinations thereofand at least one citrate ligand and include Cu(C₆H₇O₇), Cu₂(C₆H₄O₇),Cu₃(C₆H₅O₇) or Cu(C₆H₇O₇)₂. In another example, copper EDTA may includeat least one cupric atom, cuprous atom or combinations thereof and atleast one EDTA ligand and include Cu(C₁₀H₁₅O₈N₂), Cu₂(C₁₀H₁₄O₈N₂),Cu₃(C₁₀H₁₃O₈N₂), Cu₄(C₁₀H₁₂O₈N₂) or Cu₂(C₁₀H₁₂O₈N₂). Examples ofsuitable copper source compounds include copper sulfate, copperpyrophosphate and copper fluoroborate.

The plating solution contains one or more chelating or complexingcompounds that include compounds having one or more functional groupsselected from the group of carboxylate groups, hydroxyl groups, alkoxyl,oxo acids groups, mixture of hydroxyl and carboxylate groups andcombinations thereof. Further examples of suitable chelating compoundsinclude compounds having one or more amine and amide functional groups,such as ethylenediamine (ED), diethylenetriamine, diethylenetriaminederivatives, hexadiamine, amino acids, ethylenediaminetetraacetic acid(EDTA), methylformamide or combinations thereof. The plating solutionmay include one or more chelating agents at a concentration in the rangefrom about 0.02 M to about 1.6 M.

The one or more chelating compounds may also include salts of thechelating compounds described herein, such as lithium, sodium,potassium, cesium, calcium, magnesium, ammonium and combinationsthereof. The salts of chelating compounds may completely or onlypartially contain the aforementioned cations (e.g., sodium) as well asacidic protons, such as Na_(x)(C₆H_(8-x)O₇) or Na_(x)EDTA, whereasX=1-4. Such salt combines with a copper source to produce NaCu(C₆H₅O₇).Examples of suitable inorganic or organic acid salts include ammoniumand potassium salts or organic acids, such as ammonium oxalate, ammoniumcitrate, ammonium succinate, monobasic potassium citrate, dibasicpotassium citrate, tribasic potassium citrate, potassium tartrate,ammonium tartrate, potassium succinate, potassium oxalate, andcombinations thereof. The one or more chelating compounds may alsoinclude complexed salts, such as hydrates (e.g., sodium citratedihydrate).

Wetting agents or suppressors may be added to the solution in a rangefrom about 10 ppm to about 2,000 ppm, preferably in a range from about50 ppm to about 1,000 ppm. Suppressors include polyacrylamide,polyacrylic acid polymers, polycarboxylate copolymers, polyethers orpolyesters of ethylene oxide and/or propylene oxide (EO/PO), coconutdiethanolamide, oleic diethanolamide, ethanolamide derivatives orcombinations thereof.

One or more pH-adjusting agents are optionally added to the platingsolution to achieve a pH≧7.0, preferably between about 7.0 and about9.5. The amount of pH adjusting agent can vary as the concentration ofthe other components is varied in different formulations. Differentcompounds may provide different pH levels for a given concentration, forexample, the composition may include between about 0.1% and about 10% byvolume of a base, such as potassium hydroxide, ammonium hydroxide orcombinations thereof, to provide the desired pH level. The one or morepH adjusting agents may also include acids, including carboxylic acids,such as acetic acid, citric acid, oxalic acid, phosphate-containingcomponents including phosphoric acid, ammonium phosphates, potassiumphosphates, inorganic acids, such as sulfuric acid, nitric acid,hydrochloric acid and combinations thereof.

In an exemplary direct plating process using a Cu-ED alkalineelectrolyte, a constant cathodic current is applied to the substrateresulting in a constant current density which may be in a range betweenabout 1 mA/cm² to about 10 mA/cm² for a time period between about 0.1seconds and 5.0 seconds. This results in the formation of a copper seedlayer between about 50 Å and about 300 Å thick on the barrier layer.

Alternately, in order to ensure that a uniform, void-free seed layer isformed on a substrate during the above-described direct plating process,a “nucleation spike” or “nucleation pulse” may be used when thesubstrate surface is first brought in contact with the plating solution.“Nucleation spike” or “nucleation pulse,” as used herein, is defined asan initial higher plating current level intended to help the nucleationof the copper deposition on the substrate surface, wherein the initialplating current is at least equal to, or ideally greater than, the CCD.This plating current may exceed the maximum plating current thattypically allows for bottom-up gapfill of substrate features andtherefore is only applied for a short time. For example, in the case ofplating a copper seed layer onto a ruthenium barrier layer, a constantplating current in the range of about 5 mA/cm² to about 20 mA/cm² isapplied to the barrier layer during the nucleation pulse for about 0.1to about 5 seconds. This allows the formation of a conformal, uniformand void-free layer on the substrate, such as seed layer 111, as shownin FIG. 2.

Plating on Copper Seed with a Complex Alkaline Electrolyte

Aspects of the invention teach the use of a complex alkaline electrolytefor plating a gapfill layer, such as gapfill layer 112 (see FIG. 2),onto a seed layer, such as seed layer 111, that has been directlydeposited on a barrier layer via an alkaline solution ECP process. Thisprocess may be performed in an electrochemical plating cell similar tothe electrochemical processing cell described below in conjunction withFIG. 5.

This process is similar to that described above for direct plating on abarrier layer with a complex alkaline electrolyte. Process parametersare believed to enhance the bottom-up gapfill process, however,including plating current and deposition time. Generally, higherdeposition rates and, hence, plating current densities, may be utilizedfor this process.

The bath used for this process is also similar to that used for directplating. The complex alkaline bath for gapfill contains at least onecopper source compound and at least one complexing compounds, asdetailed previously. The one or more complexing compounds may alsoinclude salts of the chelating compounds, listed above. The bath alsomay contain wetting agents and one or more pH-adjusting agents (seeabove). Concentrations of the bath's components are believed to enhancethe bottom-up gapfill process.

Additionally, the use of a nucleation pulse is unnecessary for theformation of a uniform, void-free metal layer to be formed on the seedlayer.

Plating on Copper Seed with an Acidic Electrolyte

Aspects of the invention teach the use of a conventional acidelectrolyte for plating a gap fill layer onto a seed layer that has beendirectly deposited on a barrier layer via an alkaline solution ECPprocess. ECP gapfill deposition of copper onto a copper seed layer usingan acidic plating solution is well known in the art and may be performedin an electrochemical plating cell similar to the copper plating celldescribed below in conjunction with FIGS. 4 and 5. This process may alsobe used for depositing a copper overfill layer on a substrate, such asoverfill layer 113, in FIG. 2.

A conventional, i.e., non-complex, electrochemical plating solution forECP generally includes a copper source, an acid source, a chlorine ionsource, and at least one plating solution additive, i.e., levelers,suppressors, accelerators, antifoaming agents, etc. For example, theplating solution may contain between about 30 g/l and about 60 g/l ofcopper, between about 10 g/l to about 50 g/l of sulfuric acid, betweenabout 20 and about 100 ppm of chlorine ions, between about 5 and about30 ppm of an additive accelerator, between about 100 and about 1000 ppmof an additive suppressor, and between about 1 and about 6 ml/l of anadditive leveler. The plating current may be in the range from about 2mA/cm² to about 10 mA/cm² for filling about 300 Å to about 3000 Å copperinto the submicron trench and/or via structure. A substantially similarprocess is used for an overfill plating process, in which an additional5000 Å to 10,000 Å of copper is plated on to a substrate to complete acopper interconnect layer. Examples of copper plating chemistries andprocesses can be found in commonly assigned U.S. patent application Ser.No. 10/616,097, titled “Multiple-Step Electrodeposition Process ForDirect Copper Plating On Barrier Metals”, filed on Jul. 8, 2003, andU.S. patent application NO. 60/510,190, titled “Methods And ChemistryFor Providing Initial Conformal Electrochemical Deposition Of Copper InSub-Micron Features”, filed on Oct. 10, 2003.

Exemplary Plating Apparatus

Electrochemical Processing System

FIG. 4 is a top plan view of an embodiment of an electrochemicalprocessing system (ECPS) 400 capable of implementing the methodology ofthe present invention. The ECPS 400 generally includes a processing base413 having a robot 420 centrally positioned thereon. The robot 420generally includes one or more robot arms 422 and 424 configured tosupport substrates thereon. Additionally, the robot 420 and the robotarms 422 and 424 are generally configured to extend, rotate andvertically move so that the robot 420 may insert and remove substratesto and from a plurality of processing locations 402, 404, 406, 408, 410,412, 414 and 416 positioned on the base 413. Processing locations may beconfigured as electroless plating cells, electrochemical processingcells, substrate rinsing and/or drying cells, substrate bevel cleancells, substrate surface clean or preclean cells and/or other processingcells that are advantageous to plating processes. Preferably,embodiments of the present invention are conducted within at least oneof the processing locations 402, 404, 406, 408, 410 and 412.

The ECPS 400 further includes a factory interface, or FI 430. The FI 430generally includes at least one FI robot 432 positioned adjacent oneside of the FI 430 that is adjacent to the processing base 413. The FIrobot 432 is positioned to access a substrate 426 from substratecassettes 434. The FI robot 432 delivers the substrate 426 to one ofprocessing locations 414 and 416 to initiate a processing sequence.Similarly, FI robot 432 may be used to retrieve substrates from one ofthe processing locations 414 and 416 after a substrate processingsequence is complete. In this situation FI robot 432 may deliver thesubstrate 426 back to one of the cassettes 434 for removal from thesystem 400. Further, robot 432 also extends into a link tunnel 415 thatconnects factory interface 430 to processing mainframe or platform 413.Additionally, FI robot 432 is configured to access an anneal chamber 435positioned in communication with the FI 430.

Electrochemical Plating Cell

FIG. 5 illustrates a partial perspective and sectional view of anexemplary electrochemical processing cell, hereinafter referred to asplating cell 500, that may be implemented in processing locations 402,404, 406, 408, 410, 412, 414, 416 of FIG. 4. The plating cell 500generally includes a plating head assembly 600, a frame member 503, anouter basin 501 and an inner basin 502 positioned within outer basin501.

The plating head assembly 600 includes a receiving member 601forsupporting and rotating a substrate during immersion into theelectrochemical processing solution and during electrochemicalprocessing. In this example, receiving member 601 includes a contactring 602 and a thrust plate assembly 604 that are separated by a loadingspace 606. The contact ring 602 may be adapted to make electricalcontact around the periphery of the substrate so that the necessaryelectrical bias may be applied to the substrate. The contact ring 602may be further adapted to include a reference electrode that is locatedclose to the substrate surface. A more detailed description of thecontact ring 602 and thrust plate assembly 604 may be found in commonlyassigned U.S. patent application Ser. No. 10/278,527, filed on Oct. 22,2002 and entitled “Plating Uniformity Control By Contact Ring Shaping”,and commonly assigned U.S. Pat. No. 6,251,236 entitled Cathode ContactRing for Electrochemical Deposition, both of which are herebyincorporated by reference in their entirety to the extent notinconsistent with the present invention.

The frame member 503 of plating cell 500 supports an annular base member504 on an upper portion thereof. Since frame member 503 is elevated onone side, the upper surface of base member 504 is generally tilted fromthe horizontal at an angle that corresponds to the tilt angle of framemember 503 relative to a horizontal position. Base member 504 includes adisk-shaped anode 505. Plating cell 500 may be positioned at a tiltangle, i.e., the frame portion 503 of plating cell 500 may be elevatedon one side such that the components of plating cell 500 are tiltedbetween about 3° and about 30°.

Inner basin 502 is generally configured to contain a processingsolution, such as a plating solution or a cathodic pre-treatmentsolution, during electrochemical processing of substrates. Duringprocessing, the processing solution is generally continuously suppliedto inner basin 502, and therefore, the processing solution continuallyoverflows the uppermost point 502 a, generally termed a “weir”, of innerbasin 502 and is collected by outer basin 501 and drained therefrom forchemical management and recirculation. The exemplary electrochemicalprocessing cell is further illustrated in commonly assigned U.S. patentapplication Ser. No. 10/268,284, filed on Oct. 9, 2002, and entitled“Electrochemical Processing Cell”, claiming priority to U.S. ProvisionalApplication Ser. No. 60/398,345, which was filed on Jul. 24, 2002, bothof which are incorporated herein by reference in their entireties.

In an exemplary electrochemical process, such as substrate processsequence 610, described below in conjunction with FIG. 6, a substratemay be transferred into an electrochemical processing cell, such asplating cell 500 for example, and positioned face-down on contact ring602. Thrust plate assembly 604 holds the substrate in place duringprocessing. The substrate is then immersed in the electrolyte solutionfilling inner basin 502, typically while being rotated by the contactring 602 between about 5 rpm and about 60 rpm. The electrolyte solutionmay comprise an acidic, copper free solution, a complexed-copperalkaline solution, or a conventional acidic copper-containing solution,depending on the process being performed on the substrate. The substratemay be rotated between about 10 rpm and about 100 rpm during processingstep by contact ring 602. The time required for processing is dependenton each particular process, such as cathodic pre-treatment, seed layerdeposition, seed layer and gapfill layer deposition, etc. Once theprocessing step is complete, the bias is then removed and the substrateis positioned above the electrolyte solution and uppermost point 502 aof inner basin 502 for removal from plating cell 500. Prior to removalfrom plating cell 500, the substrate may be rotated between about 100and 1000 rpm for between about 1 second and about 10 seconds in order toremove excess solution from the substrate.

FIG. 6 is a flow chart of a substrate process sequence 610. Embodimentsinclude a method for depositing a metal layer onto a barrier and/oradhesion layer on a substrate that includes:

A cathodic pre-treatment 611 of the barrier or adhesion layer in anacid-containing bath.

Seed layer deposition 612 of a continuous, void-free seed layer onto thecathodically pre-treated layer.

Gapfill layer deposition 613 of a gapfill layer on the seed layer.

Optional overfill deposition 614 of an ECP overfill layer.

In one embodiment, a cathodic pre-treatment 611 of a substrate surface,such as conductive substrate surface 114 in FIG. 2, is performed. Asnoted above, the cathodic pre-treatment 611 may reduce the criticalcurrent density required to form a uniform, void-free, conformal metallayer on a barrier layer.

Next, seed layer deposition 612 takes place on the substrate, wherein aseed layer, such as seed layer 111 in FIG. 2, is directly plated ontoconductive substrate surface 114 using an electrochemical process with acomplex alkaline bath. In one aspect, a nucleation pulse is used toimprove the quality of the seed layer. In one aspect, the cathodicpre-treatment 611 and seed layer deposition 612 are performed on thesame electrochemical processing system, such as ECPS 400, describedabove in conjunction with FIG. 4, reducing the exposure time of thecathodically treated surface to oxygen and ambient contamination tominutes or even seconds. This minimizes the formation of unwanteddeposits on the treated barrier layer surface prior to seed layerdeposition.

Gapfill layer deposition 613 then takes place on the substrate, whereina gapfill layer, such as gapfill layer 112 in FIG. 2, is plated ontoseed layer 111 using the electrochemical gapfill process with a complexalkaline bath described above. In one aspect, the seed layer deposition612 and the gapfill layer deposition 613 are performed sequentially inthe same plating cell using the same plating solution. This isespecially useful for gapfill of interconnect features smaller than 65nm; such small interconnect features are particularly sensitive to theformation of voids during gapfill as well as the presence of unwanteddeposits at the interface between the seed layer and the gapfill layer.Because a single bath is used for both process steps, the surface of theseed layer is never exposed to atmosphere prior to gapfill layerdeposition 613, eliminating the possibility of unwanted oxidation.Further, there is virtually no time for organic contaminants toaccumulate on the seed layer surface since the seed layer deposition 612may be followed immediately by the gapfill layer deposition 613.

An overfill deposition 614 then may be performed on the substrate,wherein an ECP overfill layer, such as overfill layer 113, may bedeposited to complete formation of an interconnect layer. In one aspect,the overfill deposition 614 is performed sequentially in the sameplating cell as gapfill deposition 613, using the same plating solution.This avoids oxidation and organic contamination of the gapfill layerprior to overfill deposition 614. In another aspect, the overfilldeposition 614 is performed via a conventional acidic electrolyte ECPprocess. In this aspect, an additional rinsing step is performed on thesubstrate between the gapfill layer deposition 613 and the overfilldeposition 614 to prevent cross-contamination of the plating solutionused for ECP overfill. The additional rinsing step may be performed in adedicated rinsing chamber, preferably located on the sameelectrochemical processing system wherein the substrate process sequence610 may be performed. The substrate is rinsed with an aqueous solutionwhile rotating at a rate from about 20 to about 400 rpm and subsequentlydried via gas flow and/or spin-drying. Due to the inherentincompatibility of acidic and basic solutions, as well as the seriousproblems associated with cross-contamination of organic additivesbetween plating solutions, rigorous cleaning of the plating cell wouldhave to be performed between the gapfill layer deposition 613 and theoverfill deposition 614 for each substrate processed therein. Instead,it is preferred that two separate ECP cells are used to complete theformation of copper layer 110 in apertures 120 on a substrate: one celldedicated to an alkaline-based plating process, i.e., the seed layerdeposition 612 and the gapfill layer deposition 613, and one celldedicated to acid-based plating processes, i.e., the overfill deposition614. To minimize waiting time and the associated oxidation andcontamination of the gapfill layer prior to the overfill deposition 614,both ECP cells are preferably situated on the same substrate processingplatform, such as the exemplary plating system described below inconjunction with FIG. 4. The overfill deposition 614 is particularlybeneficial when there is a need to fill large and small interconnectfeatures on a substrate surface at the same time; the small or highaspect ratio interconnect features are filled during the gapfill layerdeposition 613 and the larger, low aspect ratio features are filled withthe higher deposition rate ECP overfill process.

In another embodiment, a cathodic pre-treatment 611 is performed on asubstrate surface, such as conductive substrate surface 114 in FIG. 2.As stated above in the previous embodiment, the cathodic pre-treatment611 reduces the critical current density.

Next, the seed layer deposition 612 takes place on the substrate,wherein a seed layer is directly plated onto conductive substratesurface 114 using an electrochemical process with a complex alkalinebath. In one aspect, a nucleation pulse is used to improve the qualityof the seed layer. In one aspect, the cathodic pre-treatment 611 and theseed layer deposition 612 are performed on the same electrochemicalprocessing system. In another aspect, the smallest interconnect featureson a substrate are completely filled during the seed layer deposition612, whereas only a conformal seed layer is formed on the surfaces oflarger interconnect features. As described above in the seed layerdeposition 612 of the previous embodiment, it is beneficial for thecathodic pre-treatment 611 and the seed layer deposition 612 to beperformed on the same electrochemical processing system to minimize theformation of unwanted deposits on the treated barrier layer surfaceprior to seed layer deposition.

In gapfill layer deposition 613, a gapfill layer is plated onto seedlayer 111 using an electrochemical gapfill process with a conventionalacid bath as described above. No complexing agents are necessary in thisplating process. Preferably, gapfill layer deposition 613 is performedin a different electrochemical processing cell than the seed layerdeposition 612 to isolate acid-based and alkaline-based processes. Inone aspect, an additional rinsing step is performed on the substratebetween the seed layer deposition 612 and the gapfill deposition 613 toprevent cross-contamination of the plating solution used for gapfill.The additional rinsing step is substantially similar to that describedabove in overfill deposition 614 of the previous embodiment.

In overfill deposition 614 an ECP overfill layer may be deposited tocomplete formation of an interconnect layer. In one aspect, overfilldeposition 614 is performed via a conventional acidic electrolyte ECPprocess. Overfill deposition 614 may be performed in the sameelectrochemical processing cell as gapfill layer deposition 613 toprevent oxidation and other surface contaminants form forming at theinterface between the gapfill layer and the overfill layer. In anotheraspect, overfill deposition 614 is performed on the same electrochemicalprocessing system as gapfill layer deposition 613, but in a differentelectrochemical processing cell.

This embodiment allows for gapfill of the smallest features on asubstrate during cathodic pre-treatment 611, wherein the seed layer isdeposited for larger interconnect features. Subsequently, gapfill of thelarger features as well as overfill deposition of the interconnect layermay be performed on a substrate in a single ECP cell. This methodincreases the productivity of electrochemical processing systems bycombining two process steps into a single plating cell.

Although several preferred embodiments which incorporate the teachingsof the present invention have been shown and described in detail, thoseskilled in the art can readily devise many other varied embodiments thatstill incorporate these teachings.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method for depositing copper onto a substrate surface, wherein thesubstrate surface comprises an interlayer, comprising: depositing aninterlayer on a substrate surface; pre-treating the substrate surface toremove unwanted deposits from the surface of the interlayer by acathodic treatment in an acid-containing bath to reduce a criticalcurrent density during plating; and depositing a first copper layer ontothe interlayer, wherein the first copper layer is a continuous copperlayer and wherein the process of depositing the first copper layer ontothe interlayer comprises: placing the substrate surface into contactwith a copper solution, wherein the copper solution comprises complexedcopper ions, a complexing agent and a pH equal to or greater than 7.0;and applying a first plating bias to the substrate surface.
 2. Themethod of claim 1, wherein the interlayer is selected from the groupconsisting of cobalt, titanium, titanium nitride, titanium siliconnitride, tantalum, tantalum nitride, tantalum silicon nitride, tungsten,tungsten nitride, a Ti—W alloy, ruthenium, a ruthenium-tantalum alloy,rhodium, osmium or iridium.
 3. The method of claim 1, wherein thecomplexed copper ions are selected from the group consisting of copperED, copper EDTA, copper citrate and combinations thereof.
 4. The methodof claim 1, wherein the acid-containing bath is positioned on the samecopper plating system as the copper solution.
 5. The method of claim 1,wherein the cathodic treatment is performed at a potential in the rangeof about 0 volt to about −1.0 volt.
 6. The method of claim 1, whereinthe cathodic treatment is performed at a current density in the range ofabout 0.05 mA/cm² to about 5 mA/cm².
 7. The method of claim 1, whereinthe acid-containing bath contains sulfuric acid, wherein theconcentration of the sulfuric acid is in the range between about 10 g/lto about 50 g/l.
 8. The method of claim 1, wherein the process ofapplying a first plating bias comprises plating copper onto theinterlayer with a plating current that is at least equal to a criticalcurrent density.
 9. The method of claim 8, wherein the critical currentdensity is less than 10 mA/cm².
 10. The method of claim 1, furthercomprising depositing a second copper layer onto the first copper layer,wherein the process of depositing the second copper layer comprises:placing the substrate surface into a second copper solution, wherein thesecond copper solution is acidic and includes free-copper ions; andapplying a second plating bias to the substrate surface.
 11. The methodof claim 10, further comprising: applying a third plating bias to thesubstrate surface while in contact with the second copper solution todeposit a third copper layer onto the second copper layer.
 12. Themethod of claim 1, further comprising: applying a second plating bias tothe substrate surface while in contact with the copper solution todeposit a second copper layer onto the first copper layer.
 13. Themethod of claim 1, further comprising: applying a nucleation bias to thesubstrate surface after placing the substrate surface into the coppersolution and prior to applying a first plating bias to the substratesurface, the nucleation bias being configured to generate a firstcurrent density across the substrate surface greater than a criticalcurrent density.
 14. The method of claim 2, wherein the interlayer is aninterlayer on which a discontinuous copper film has been deposited. 15.A method for depositing copper onto a substrate surface, wherein thesubstrate surface comprises an interlayer, comprising: depositing aninterlayer on a substrate surface; pre-treating the substrate surface toremove unwanted deposits from the surface of the interlayer by acathodic treatment in an acid-containing bath to reduce a criticalcurrent density during plating; depositing a first copper layer onto theinterlayer, wherein the first copper layer is a continuous copper layerand wherein the process of depositing the first copper layer onto theinterlayer comprises: placing the substrate surface into contact with acopper solution, wherein the copper solution comprises complexed copperions, a complexing agent and a pH equal to or greater than 7; andapplying a first plating bias to the substrate surface; and applying asecond plating bias to the substrate surface while in contact with thecopper solution to deposit a second copper layer onto the first copperlayer.
 16. The method of claim 15, wherein the interlayer is selectedfrom the group consisting of cobalt, titanium, titanium nitride,titanium silicon nitride, tantalum, tantalum nitride, tantalum siliconnitride, tungsten, tungsten nitride, a Ti—W alloy, ruthenium, aruthenium-tantalum alloy, rhodium, osmium and iridium.
 17. The method ofclaim 15, wherein the complexed copper ions are selected from the groupconsisting of copper ED, copper EDTA, copper citrate and combinationsthereof.
 18. The method of claim 15, further comprising: applying athird plating bias to the substrate surface while in contact with thecopper solution to deposit a third copper layer onto the second copperlayer.
 19. A method for depositing copper onto a substrate surface,wherein the substrate surface comprises a ruthenium-tantalum alloy,comprising: depositing a ruthenium-tantalum alloy on a substratesurface; and depositing a first copper layer onto the ruthenium-tantalumalloy, wherein the first copper layer is a continuous copper layer andwherein the process of depositing the first copper layer onto theruthenium-tantalum alloy comprises: placing the substrate surface intocontact with a copper solution, wherein the copper solution comprisescomplexed copper ions, a complexing agent and a pH equal to or greaterthan 7.0; and applying a first plating bias to the substrate surface.20. The method of claim 19, wherein the ruthenium-tantalum alloycontains between about 70 atomic % and about 95 atomic % of rutheniumand the balance tantalum.
 21. The method of claim 20, wherein thethickness of the ruthenium-tantalum alloy is between about 5 Å to about200 Å.
 22. The method of claim 19, wherein the complexed copper ions areselected from the group consisting of copper ED, copper EDTA, coppercitrate and combinations thereof.
 23. The method of claim 19, furthercomprising depositing a second copper layer onto the first copper layerwherein the process of depositing the second copper layer comprises:applying a second plating bias to the substrate surface while in contactwith the copper solution to deposit a second copper layer onto the firstcopper layer.